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Energy nutrition - the metabolism of carbohydrates and fats - Energy-yielding metabolism

4 important questions on Energy nutrition - the metabolism of carbohydrates and fats - Energy-yielding metabolism

NAD+ cannot pass the inner membrane of mitochondria, and therefore the NADH produced by glycolysis cannot enter the mitochondria for reoxidation. Therefore substrate shuttles are used. Name them.

- Malate-aspartate shuttle > important in heart and liver. This shuttle cannot be operated if the mitochondrial NADH:NAD+-ratio is higher than in the cytosol.
- Glycerophosphate shuttle > important in muscles.

How many ATP costs the conversion of lactate to glucose and where is this done?

It costs 6 ATP and is done by the liver. In tissues such as the heart, lactate is oxidized to pyruvate again. NADH is then again used in the mitochondrial electron transport chain.

From which sources does acetylCoA arises?

- Pyruvate decarboxylation and oxidation
- B-oxidation of fatty acids
- Ketone bodies
- Alcohol
- Amino acids that give rise to acetylCoA or acetoacetate

What are the intermediates of the citric acid cycle alfa-ketoglutarate, oxaloacetate and citrate used for?

- Alfa-ketoglutarate and oxaloacetate can give rise to amino acids glutamate and aspartate (important for the malate-aspartate shuttle and transamination needed for the urea-cycle).
- oxaloacetate is also the precursor for glucose synthesis in the fasting state (gluconeogenesis)
- Citrate is the source of AcetylCoA for fatty acid synthesis in the cytosol in the fed state.